Under steady-state engine operating conditions, the mass of air charge for each cylinder event is constant and the fuel transport mechanisms in the fuel intake have reached equilibrium. As a result, the mass of injected fuel for each cylinder event is also constant. When the operating condition is not steady-state, however, the mass of injected fuel required to achieve the desired air-fuel ratio in the cylinder is not constant. Transient operation can be due to changes in the mass of air charge, less than all of the cylinders being fueled for each event, or a desired change in the air-fuel ratio.
U.S. Pat. No. 5,746,183 describes a system for controlling fuel delivery during transient engine conditions using a series of steps. This method accomplishes improved fuel delivery by sensing a plurality of engine parameters. The method described includes the step of determining an initial base desired fuel mass based on the plurality of engine parameters. The method further includes the step of determining an initial transient fuel mass based on the prior injection history. Still further, the method includes the step of determining a desired injected fuel mass to be delivered to the individual cylinder based on the initial base desired fuel mass and the initial transient fuel mass. Finally, the method includes the step of sensing delivery of the desired injected fuel mass and determining an updated prior injection history based on the desired injected fuel mass and the prior injection history.
In engines equipped with intake manifold runner control (IMRC) systems, however, additional air-fuel control mechanisms may be required. In particular, during IMRC transitions when the engine is cold, the engine's air-fuel ratio goes lean on transitions to open the valve, and rich on transitions to close the valve. This can result in an undesirable torque `bump` relating to air-fuel ratio control.
Thus, there exists a need to improve air-fuel control during intake control device transitions by compensating for fuel transport dynamics and the actual fuel injected into each cylinder.